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Discussion Starter #1
So a few weeks ago I cleaned my carbs and put them back on. I started to notice a few weird things after that, primarily a general loss of power and a hanging/high idle when hot. After checking my idle screw settings with no change, I figured it was probably that my carbs were out of sync. So I got a carb sync tool (Motion Pro - Syncpro Carb Tuner) and made an attempt at syncing. I didn't expect that one side seems totally normal and the vacuum pulls a good amount, but the other side doesn't respond at all. I've tried multiple times with different hoses and recalibrated all the columns so I know they work.

What's the deal? I'll be pulling the carbs tonight to give them a once over again. :think: My best guesses are a bad gasket seal letting in air, an obstructed jet, or a float stuck down and not letting in enough fuel. Is there anything else that could cause this lack of vacuum pressure on one side? How bad is it to run the bike in this condition?

Thanks!!
 

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The hanging idle after you cleaned the carbs is the clue.

Hanging idle, especially in a case like this, is normally a lean condition.

Either air intake leak or block jet and/or mixture screw passage way.

And to add, did you go back to the baseline settings that you had before the cleaning?
 

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I would be looking at your carb-to-intake-tube rubbers... must be getting pretty old, baked, dry & tatty after all this time? ;)
 

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Could a diaphragm be torn or not seated properly? Also, you can do a rough synch test by placing a finger on each slide and slowly opening the throttle. You should feel them both start to move at the same time.
 

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Could a diaphragm be torn or not seated properly? Also, you can do a rough synch test by placing a finger on each slide and slowly opening the throttle. You should feel them both start to move at the same time.
this may be the case on Keihins but certainly NOT the case on stock Mikuni BSDT.

Equalizing "butterflies" using feeler gauge on stockers gets you in the ballpark.
 

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If your stock carb vent system has been modified, make sure the hoses and screens are clear. If your hoses are old, replace them with fuel line. Spring reinforcement around hoses must be there to avoid collapse. I replaced my vent screens with small motorcycle fuel filters to eliminate dirt in the diaphragm housings. Make sure your diaphragm covers are flat in the sealing area. Mine were not. Change the little o rings that seal the air passages to the covers. Check for flatness of the manifold flanges, mine were not flat. Plug the diaphragm hose inlet and see if the diaphragms are leaking. They should not drop free with the hole plugged. Don't leave your covers off too long or diaphragms may not fit in the groove correctly, which is critical. Check for cracks or pin holes in diaphragms.
 

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Discussion Starter #7
Thanks for all the responses! You all are the greatest resource on the internets!

This is going to make me look like a total noob, but I guess that's technically what I am. I'm writing my findings here in hopes that if someone else has the same problem they can maybe have another thing to check for

In disassembling my carbs to clean them (it was the first time I'd ever even really laid eyes on carbs), I was careful to make sure I didn't lose anything and painstakingly clean everything. However, upon reassembly I ended up with one smallish spring left over that I couldn't figure out where it belonged. So I bagged it up and decided to re-install the carbs and see if it would work. And it did! Only with a few problems I mentioned before. The carbs were super messed up before (floats sticking, high idle, leaky, etc etc), so I didn't have a good baseline for knowing what was normal. In fact my first post here was asking what exactly is 'normal'.

Anyway, today, after taking my carbs off and just sitting there playing with them for a while I found that the sync screw no matter what it's position wouldn't actually affect the position of either butterfly valve. It seemed like the where the two pulleys meet at the throttle, they should have been making contact much earlier than they were. This was causing one valve to open long before the other.

Then it clicked, I had saved that extra spring and it was just about the right size to fit between two plates on either pulley and bridge the gap. And violá! Now the slightest adjustment to the sync valve alters the relative actions of the valves and they both respond simultaneously like I imagine they should. Somehow every tutorial and manual I've read never mentioned this spring (or I overlooked them all)!

Now I say all this, but I won't' be able to reinstall the carbs until morning, so i'm only guessing that I figured it out. But it's so consistent with the problems I've been having that it's at least my biggest problem. I'm going to put money on this being solved, but I'll let y'all know. Just in time for a big weekend trip too :)

Glad I didn't lose that spring!
 

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Thanks for all the responses! You all are the greatest resource on the internets!

This is going to make me look like a total noob, but I guess that's technically what I am. I'm writing my findings here in hopes that if someone else has the same problem they can maybe have another thing to check for

In disassembling my carbs to clean them (it was the first time I'd ever even really laid eyes on carbs), I was careful to make sure I didn't lose anything and painstakingly clean everything. However, upon reassembly I ended up with one smallish spring left over that I couldn't figure out where it belonged. So I bagged it up and decided to re-install the carbs and see if it would work. And it did! Only with a few problems I mentioned before. The carbs were super messed up before (floats sticking, high idle, leaky, etc etc), so I didn't have a good baseline for knowing what was normal. In fact my first post here was asking what exactly is 'normal'.

Anyway, today, after taking my carbs off and just sitting there playing with them for a while I found that the sync screw no matter what it's position wouldn't actually affect the position of either butterfly valve. It seemed like the where the two pulleys meet at the throttle, they should have been making contact much earlier than they were. This was causing one valve to open long before the other.

Then it clicked, I had saved that extra spring and it was just about the right size to fit between two plates on either pulley and bridge the gap. And violá! Now the slightest adjustment to the sync valve alters the relative actions of the valves and they both respond simultaneously like I imagine they should. Somehow every tutorial and manual I've read never mentioned this spring (or I overlooked them all)!

Now I say all this, but I won't' be able to reinstall the carbs until morning, so i'm only guessing that I figured it out. But it's so consistent with the problems I've been having that it's at least my biggest problem. I'm going to put money on this being solved, but I'll let y'all know. Just in time for a big weekend trip too :)

Glad I didn't lose that spring!
That would do it! :D

Always best to be honest in these circumstances an say "I have this bit left over?", gives us more of a clue...

We've all been there. ;)
 

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Discussion Starter #9
That would do it! :D

Always best to be honest in these circumstances an say "I have this bit left over?", gives us more of a clue...

We've all been there. ;)
I would have said something, but I had done this before I joined the forums and it had slipped my mind since.

Anyway, now that everything is back in place the bike is running much better! Idling is way better, the hanging idle is gone, the engine sounds much more full and healthy, and the throttle is smooth all the way though. The bike had a lot of carb problems when I bought it a few months ago and now they seem to be mostly ironed out and it's in better shape than when I bought it. It's awesome!
 
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